This invention relates to apparatus for the plasma treatment of semiconductors and, more particularly, to apparatus for the plasma treatment of semiconductors having an improved construction which makes it possible to start a discharge quickly and assuredly.
The fabrication of semiconductor device includes the step of subjecting semiconductor substrates to plasma treatment with the aid of an electric discharge. A conventional apparatus for carrying out such plasma treatment is described below by reference to FIG. 1. The term "semiconductor" as used herein comprehends both semiconductive materials such as silicon and semiconductive compounds such as silicon nitride (Si.sub.3 N.sub.4) and silicon dioxide (SiO.sub.2).
In FIG. 1, a treatment chamber 1 has semiconductor substrates 2 placed therein. Within this treatment chamber 1, semiconductor substrates 2 are subjected to plasma treatment, such as plasma etching, in the gas-phase. The gas fed from an etching gas source 4 is introduced into treatment chamber 1 by way of a conduit 5 interconnecting etching gas source 4 and treatment 1. The etching gas is exhausted from treatment chamber 1 after the etching operation by evacuation means 3. In an intermediate portion of conduit 5 is provided a plamsa generating switch 5a, which penetrates through a part of a waveguide 7 connected to a microwave oscillator 6.
In the operation of the above-described plasma etching apparatus, the power switch is first turned on to actuate microwave oscillator 6. Then, a high-frequency electric field is applied through waveguide 7 to plasma generating section 5a, whereby a plasma discharge is started within plasma generating section 5a. It often happens, however, that the application of a high-frequency electric field causes a discharge to occur with a time lag of 1 to 10 seconds or even fails to start a discharge. If no discharge occurs upon application of a high-frequency electric field, it is necessary to cut off the high-frequency electric field and then turn on the power switch again.
Thus, the conventional plasma etching apparatus has a great difficulty in automatizing the operation of the apparatus because it is hard to determine whether a discharge has been started or not and it is sometimes required to operate the power switch over again. More specifically, the time switch for setting the desired treating time cannot be actuated before the operator goes to the trouble of confirming, for example, by visual inspection that a discharge has occurred.